Grounding of Substation DC Systems

[alingstone]

Hi

What are the advantages and disadvantages of solidly grounding the negative pole of a substation DC system. The DC system would be operating at 48V DC and would be used for protection & control systems. The ground/earth would rise as a result of AC system ground faults and the likes, but i'm thinking that this shouldn't affect the DC system.

 

[davidbeach]

Typical North American practice is to run it ungrounded, and more often 125VDC than 48VDC. With an ungrounded system, the first accidental ground can be detected but won't do anything. With a ground applied to one pole of the battery, an accidental ground elsewhere can do all sorts of mischief. It could be a hard short and blow a fuse or it could just wind up shorting around a contact or an input and depending, either cause an undesired action or prevent a desired action. Better to be ungrounded (but you'll never convince the comm guys of that) or if you absolutely think it must be grounded, ground it mid way between the positive and negative terminals. If every operation requires well over half voltage, then an accidental ground won't cause any action, but it may prevent actions.